1. Field of the Invention
This invention relates to train positioners for moving one or more railroad cars into position for loading or unloading of the cars and, more particularly, to control systems for such train positioners.
2. Background Art
The use of train positioners for automatically and sequentially moving one or more railroad cars of a multi-car unit train is well known in the art. For example, a train positioner can be used to move the railroad cars, such as open-topped hopper or gondola-type railroad cars, through a rotary car dumper. The cars are typically equipped with rotary couplings, are rotated about a longitudinal axis within the car dumper and the contents therein dumped out without being uncoupled.
A wide variety of train positioners are known in the field. See, for example, the devices disclosed in U.S. Pat. Nos. 3,212,454; 3,260,220; 3,262,399; 3,695,185; 3,942,451; 4,006,691; 4,038,927; 4,354,792; 4,512,260; 4,637,316; and 4,926,755. A typical train positioner is shown in U.S. Pat. No. 3,212,454 and includes an elongated carriage trackway positioned along one side of the train tracks and, typically, upstream of a dumping station or the like. A positioner carriage is moved along the carriage track in a controlled manner and carries thereon a positioner arm which can be moved into and out of engagement with a coupler between adjacent railroad cars. With the positioner arm in a vertical position, the positioner is moved to an initial or starting location on the carriage trackway. The positioner arm is then moved to a substantially horizontal position in contact with the coupler. The positioner carriage is then moved along the carriage trackway and, through the contact of the positioner arm with the coupler, moves the entire unit train along the train tracks through a predetermined distance, typically one or more train car lengths. After the positioner carriage has stopped at a final location, the positioner arm is moved to a vertical position out of contact with the coupler and the positioner carriage is returned to the starting location. The cycle described above is repeated sequentially and automatically until the entire train has been moved through the dumping station.
In a typical control operation, the positioner carriage is moved from a stopped mode at the starting location, through an acceleration period and then to a constant, running speed. The positioner carriage is then moved along the carriage trackway at the constant running speed until a preset location or point is reached for initiating deceleration. This preset point is typically identified by a limit switch which sends a control signal to an appropriate controller or the like. The positioner carriage is then slowed through a deceleration mode at a predetermined rate until the positioner carriage reaches and is stopped at the final location on the carriage trackway. The initial and final locations of the positioner carriage along the carriage trackway are typically identified by limit switches or the like.
One of the drawbacks with a preset or fixed deceleration point and rate system is that the deceleration point must be placed far enough upstream of the final location so that the positioner carriage can adequately stop the train during the most severe loads, i.e., when the train is fully loaded and at its greatest mass. However, the mass of the train actually changes from cycle to cycle as the individual railroad cars are either loaded or unloaded. For example, as the train becomes lighter during continued unloading of cars, the preset deceleration point provides a deceleration distance longer than is needed to stop the train. This gap between the preset deceleration distance and that actually needed to stop the train becomes even longer as the train is further unloaded and, hence, lightened in weight. Substantial operation time is wasted by fixing the deceleration distance at a constant and maximum length to cover the extreme train weight which exists for only a short period of time.
In addition, the forces to which the positioner arm is subjected during the acceleration and, particularly, deceleration operations can be rather severe. This was not a great problem when unit trains used conventional absorbing or slack-type couplings. The couplings in the train would absorb most if not all of the excess energy when the train was decelerated by the positioner. However, the trend in modern trains is to use more rigid or slackless couplings in which there is little or no give or free play between the attached railroad cars. Therefore, all of the energy which must be dissipated during the deceleration mode of operation is imparted on the positioner and its coupling arm. For prior positioners designed with a fixed deceleration point arrangement and for conventional couplings, the positioners often cannot withstand the forces to which they are subjected from unit trains using slackless couplings.
A variety of positioning and motor control systems are known in the art. See, for example, U.S. Pat. Nos. 3,312,886; 4,078,191; 4,181,197; 4,225,813; 4,460,862; 4,777,420; 4,864,211; and 4,914,366. However, none of these references provide any teachings which would overcome the disadvantages with the known train positioners as discussed above.
Therefore, it is an object of the present invention to overcome the disadvantages of the prior train positioner control arrangements. In particular, it is an object of the present invention to provide a train positioner in which the deceleration point and deceleration rate are set in accordance with the changing demands from the changes of the train during operation. In addition, it is an object of the present invention to dissipate all or substantially all of the energy of the train during the deceleration operation so that the positioner is not subject to excessive or damaging forces.